Aluminum alloy for die casting, and aluminum alloy die-cast product using same

ABSTRACT

Provided are: an aluminum alloy for die casting, having castability and mechanical properties equivalent to those of ADC12 and corrosion resistance equivalent to that of ADC6; and an aluminum alloy die cast obtained through die-casting the alloy. Specifically, the present invention is directed to an aluminum alloy for die casting that contains: Cu by not more than 0.10 wt %; Si by 12.0 to 15.0 wt %; Mg by not more than 1.00 wt %; Fe by 0.05 to 1.00 wt %; Cr by 0.10 to 0.50 wt %; and a remaining portion thereof being Al and unavoidable impurities.

TECHNICAL FIELD

The present invention relates to an aluminum alloy for die casting having improved castability and corrosion resistance, and an aluminum alloy die cast produced using the alloy.

BACKGROUND ART

Aluminum alloys are lightweight and have various properties such as excellent thermal conductivity and high corrosion resistance, and therefore are widely used as materials for components in various fields such as automobiles, industrial machines, aircrafts, and electrical home appliances. One of such fields is the field of aluminum alloys for die casting, and representative examples thereof include ADC12 that is an Al—Si—Cu based alloy for die casting specified by Japanese Industrial Standards JIS H5302 (hereinafter simply referred to as “ADC12”). ADC12 has satisfactory fluidity and filling characteristic during casting (die casting), and therefore has been frequently used for usage applications such as cases and covers such as cylinder head covers, cylinder blocks, and carburetors for automobiles, or die cast components other than those for automobiles.

However, since ADC12 is poor in corrosion resistance, a process for improving corrosion resistance, such as anodic oxidation, is required if ADC12 is used under an environment where it is easily corroded, which causes problems in terms of labor, cost, and the like.

In contrast, ADCS and ADC6 that are Al—Mg based alloys for die casting specified by Japanese Industrial Standards JIS H5302 (hereinafter simply referred to as “ADCS” and “ADC6”) are excellent in corrosion resistance, but are poor in fluidity because of a large solidification range and therefore are likely to cause cracks in die-cast products. That is, since the Al—Mg based alloys are significantly inferior in castability to ADC12, usage applications thereof are likely to be disadvantageously limited to products with simple structures.

Hence, as a technology for providing an aluminum alloy for die casting having excellent castability and corrosion resistance, Patent Literature 1 discloses an aluminum alloy for die casting that contains: Si by 9.0 to 12.0 wt %; Mg by 0.20 to 0.80 wt %; Mn+Fe by 0.7 to 1.1 wt %, in which Mn/Fe ratio is not less than 1.5; Cu as an impurity that is regulated to be not more than 0.5 wt %; and a remaining portion of the aluminum alloy that consists of aluminum and unavoidable impurities.

According to this technology, among the amounts of the components of the aluminum alloy for die casting, the amounts of Mn, Fe, and Cu have great influence on corrosion resistance of the aluminum alloy, and the corrosion resistance is greatly improved as compared to that of ADC12 by, for example, regulating the amount of Cu to be not more than 0.5 wt %.

CITATION LIST Patent Literature

[PTL 1] Japanese Laid-Open Patent Publication No. 2006-183122

SUMMARY OF INVENTION Technical Problem

However, the conventional technology described above has the following drawbacks.

That is, although the technology disclosed in Patent Literature 1 can improve corrosion resistance of an aluminum alloy to a level approximately equal to that of AC4C that is an Al—Si—Mg based alloy for die casting specified by Japanese Industrial Standards JIS H5202, mechanical properties of the aluminum alloy in comparison with ADC12 are uncertain.

Further, although the technology disclosed in Patent Literature 1 provides castability about 80% of that of ADC12 when compared in flow length, it is difficult to say that the castability reaches a level approximately equal to that of ADC12.

Thus, a main objective of the present invention is to provide: an aluminum alloy for die casting, having castability and mechanical properties equivalent to those of ADC12 and corrosion resistance equivalent to that of ADC6; and an aluminum alloy die cast produced using the alloy.

Solution to Problem

A first aspect of the present invention is an aluminum alloy for die casting “containing: Cu by not more than 0.10 wt %; Si by 12.0 to 15.0 wt %; Mg by not more than 1.00 wt %; Fe by 0.05 to 1.00 wt %; Cr by 0.10 to 0.50 wt %; and a remaining portion thereof being Al and unavoidable impurities”.

In the present invention, Si is contained by 12.0 to 15.0 wt % to improve castability of the alloy, the content ratio of Cu that is considered to have most influence on corrosion resistance is suppressed to not more than 0.10 wt %, and Cr that effectively improves corrosion resistance and anti-seizing characteristic is contained by 0.10 to 0.50 wt %. Therefore, it is possible to obtain an alloy having castability and mechanical properties comparable to those of ADC12, and high corrosion resistance comparable to that of ADC6.

As described above, in the present invention, by simply containing the five types of elemental components at the predetermined ratio, an ingot of an aluminum alloy for die casting having not only excellent castability and mechanical properties but also excellent corrosion resistance can be produced safely and easily.

With respect to the aluminum alloy for die casting of the present invention, preferably, at least one selected from Na, Sr, and Ca is added by 30 to 200 ppm, or Sb is added by 0.05 to 0.20 wt %. By doing so, it is possible to reduce the size of particles of eutectic Si and further improve strength and toughness of the aluminum alloy.

In addition, adding Ti by 0.05 to 0.30 wt % or adding B by 1 to 50 ppm is also preferable. By doing so, crystal grains of the aluminum alloy can be miniaturized even when the amount of Si is particularly small and when a casting method having a low cooling rate is used. As a result, stretching of the aluminum alloy can be improved.

A second aspect of the present invention is an aluminum alloy die cast obtained through die-casting the aluminum alloy for die casting according to the first aspect.

Since the aluminum alloy die cast obtained through die-casting the aluminum alloy for die casting of the present invention can be mass produced with satisfactory castability and is superior not only in mechanical properties such as yield strength and stretching but also in corrosion resistance, the aluminum alloy die cast is most suitable for usage applications, such as structural components for automobiles, which are used outdoor for long hours.

Advantageous Effects of Invention

According to the present invention, it is possible to provide: an aluminum alloy for die casting, having castability and mechanical properties equivalent to those of ADC12 and corrosion resistance equivalent to that of ADC6; and an aluminum alloy die cast produced using the alloy.

DESCRIPTION OF EMBODIMENTS

In the following, an embodiment of the present invention will be described in detail with specific examples.

An aluminum alloy for die casting of the present invention (hereinafter, also simply referred to as “aluminum alloy”) mainly contains Cu (copper) by not more than 0.10 wt %, Si (silicon) by 12.0 to 15.0 wt %, Mg (magnesium) by not more than 1.00 wt %, Fe (iron) by 0.05 to 1.00 wt %, Cr (chromium) by 0.10 to 0.50 wt %, and Al (aluminum) and unavoidable impurities as a remaining portion of the aluminum alloy. Hereinafter, the properties of each of the elements will be described.

Cu (copper) improves mechanical strength and hardness of the aluminum alloy, but on the other hand, significantly degrades corrosion resistance of the aluminum alloy. Therefore, in order to improve corrosion resistance of the aluminum alloy, the content of Cu, except Cu mixed as an impurity, needs to be reduced.

Hence, in the present invention, in order to enable use of scraps as raw materials for the aluminum alloy, the content ratio of Cu with respect to the whole weight of the aluminum alloy is not more than 0.10 wt %. If more strict corrosion resistance is required of the aluminum alloy die cast using the alloy, the content ratio of Cu with respect to the whole weight of the aluminum alloy is preferably not more than 0.08 wt %, and more preferably, not more than 0.05 wt %.

Si (silicon) is an important element that contributes to improvement of fluidity, reduction in liquidus temperature, and the like when the aluminum alloy is molten, thereby to improve castability.

The content ratio of Si with respect to the whole weight of the aluminum alloy is preferably within a range of 12.0 to 15.0 wt % as described above. When the content ratio of Si is less than 12.0 wt %, melting temperature and casting temperature of the aluminum alloy increase, and sufficient fluidity cannot be ensured during die casting since fluidity of the aluminum alloy reduces when the aluminum alloy is molten. Also when the content ratio of Si is more than 15.0 wt %, castability is degraded due to reduced fluidity and increased liquidus temperature.

Mg (magnesium) mainly exists as Mg2Si or in a solid-solution state in an Al base material in the aluminum alloy, and is a component that provides yield strength and tensile strength to the aluminum alloy but, when being contained by an excessive amount, has an adverse effect on castability and corrosion resistance.

The content ratio of Mg with respect to the whole weight of the aluminum alloy is preferably within a range not more than 1.00 wt % as described above. The presence of Mg within the above range can improve mechanical properties of the aluminum alloy such as yield strength and tensile strength, without greatly affecting corrosion resistance. When the content ratio of Mg is more than 1.00 wt %, stretching of the alloy is reduced, which results in degraded quality of an aluminum alloy die cast produced by using the alloy.

Fe (iron) is known to have a seizing prevention effect during die casting. However, Fe causes crystallization of a needle like crystal in the form of Al-Si-Fe, reduces toughness of the aluminum alloy, and, when being added in a large quantity, causes melting at a suitable temperature to be difficult.

The content ratio of Fe with respect to the whole weight of the aluminum alloy is preferably within a range of 0.05 to 1.00 wt % as described above. When the content ratio of Fe is less than 0.05 wt %, the seizing prevention effect during die casting becomes insufficient, whereas when the content ratio of Fe is more than 1.00 wt %, although the seizing prevention effect becomes sufficient, toughness of the alloy reduces and the melting temperature rises to cause degradation of castability.

Cr (chromium) mainly exists in a molten state when the aluminum alloy is molten, and when the aluminum alloy is solid, exists in a solid-solution state in an Al phase or in a crystallized state as a Cr based compound. Similar to Fe and Mn described above, Cr is used for preventing seizing of the aluminum alloy and a mold during die casting, and for improving corrosion resistance of the alloy.

The content ratio of Cr with respect to the whole weight of the aluminum alloy is preferably within the range of 0.10 to 0.50 wt % as described above. When the content ratio of Cr is less than 0.10 wt %, the effect of improving corrosion resistance of the alloy becomes insufficient, whereas when the content ratio of Cr is more than 0.50 wt %, although corrosion resistance becomes sufficient, liquidus temperature increases and fluidity reduces to cause degradation of castability.

When the content ratios of Cu, Si, Mg, Fe, and Cr are adjusted in accordance with the content ratios described above, it is possible to obtain a base metal of an aluminum alloy for die casting having, with a highly safe but simple formulation, castability and mechanical properties equivalent to those of ADC12 and corrosion resistance equivalent to that of ADC6.

In addition to the elemental components described above, at least one element selected from Na (sodium), Sr (strontium), Ca (calcium), and Sb (antimony) may be added as a modification material. By adding such a modification material, it is possible to reduce the size of eutectic Si particles, and further improve toughness and strength of the aluminum alloy.

The addition ratio of the modification material with respect to the whole weight of the aluminum alloy is preferably within a range of 30 to 200 ppm when the modification material is Na, Sr, and Ca, and within a range of 0.05 to 0.20 wt % when the modification material is Sb. When the addition ratio of the modification material is less than 30 ppm (0.05 wt % in the case with Sb), miniaturizing eutectic Si particles in the aluminum alloy becomes difficult, whereas when the addition ratio of the modification material is more than 200 ppm (0.20 wt % in the case with Sb), eutectic Si particles in the aluminum alloy are sufficiently miniaturized, and no further addition effect can be obtained even when the added amount is increased.

Furthermore, at least one of Ti (titanium) and B (boron) may be added instead of or together with the modification material. By adding at least one of Ti and B in such manner, crystal grains of the aluminum alloy are miniaturized, and stretching of the alloy can be improved. It should be noted that such an advantageous effect becomes significant when the amount of Si is particularly small or when a casting method having a low cooling rate is used.

The addition ratios of Ti and B with respect to the whole weight of the aluminum alloy are preferably within a range of 0.05 to 0.30 wt % and a range of 1 to 50 ppm, respectively. When the addition ratio of Ti is less than 0.05 wt % or the addition ratio of B is less than 1 ppm, miniaturizing the crystal grains in the aluminum alloy becomes difficult, whereas when the addition ratio of Ti is more than 0.30 wt % or the addition ratio of B is more than 50 ppm, the crystal grains in the aluminum alloy are sufficiently miniaturized, and no further addition effect can be obtained even when the added amount is increased.

When the aluminum alloy for die casting according to the present invention is to be produced, first, a raw material designed to contain, at the predetermined ratio described above, each of the elemental components of Al, Cu, Si, Mg, Fe, and Cr is prepared. Next, the raw material is placed in a melting furnace such as a sealed melting furnace or a melting furnace with a fore hearth to melt the elemental components. The molten raw material, i.e., the molten metal of the aluminum alloy is subjected to refinement treatments such as a dehydrogenation treatment and an inclusion removal treatment, if necessary. Then, the refined molten metal is casted in a predetermined mold and solidified in order to form the molten metal of the aluminum alloy into an alloy base metal ingot or the like.

Furthermore, after producing the aluminum alloy die cast using the aluminum alloy for die casting according to the present invention, a solution treatment and an aging treatment, etc., are performed if necessary. By performing the solution treatment and the aging treatment on the aluminum alloy die cast in such manner, mechanical properties of the aluminum alloy cast can be improved.

EXAMPLES

In the following, the present invention will be described specifically by means of Examples, but the present invention is not limited to the Examples.

Mechanical properties (tensile strength, stretching, and 0.2%-yield strength) in predetermined Examples and Comparative Examples were measured by a method described below. Specifically, by using an ordinary die casting machine (DC135EL manufactured by Toshiba Machine Co., Ltd.) having a clamping force of 135 ton, die casting was performed at an injection speed of 1.0 m/s with a casting pressure of 60 MPa to produce a round bar test piece that is in compliance with ASTM (American Society for Testing and Material) standard. Then, tensile strength, stretching, and 0.2%-yield strength were measured for the round bar test piece in the as-cast condition by using a universal testing machine (AG-IS 100kN) manufactured by Shimadzu Corp.

In addition, corrosion resistance was evaluated with a (neutral) salt spray test that is compliant with Japanese Industrial Standards JIS2371.

Further, castability during die casting was evaluated by the following method, in addition to measuring liquidus temperature of the alloy. That is, the alloy ingot was molten, and a flow length of the solution was measured at a temperature 100° C. higher than the alloy liquidus temperature. An MIT fluidity testing machine was used for the measurement. The conditions for the MIT testing machine were as follows. A set value for differential pressure of a vacuum pump was 200 Torr (gauge pressure). A Pyrex suction tube (“Pyrex” is registered trademark) having an inner diameter of φ5 mm (L-shaped tube) was used. The average of n=5 was calculated as a flow length of the alloy.

Table 1 shows the elemental compositions, salt spray measurement results, and mechanical properties of aluminum alloys, which are the objects of the present invention, in Examples 1 to 9 and Comparative Examples 1 to 9.

TABLE 1 Physical Property Salt measurement result spray test 0.2%- Elemental composition result Tensile Stretch- yield (wt %) (mg/dm²/ strength ing strength Cu Si Mg Fe Cr day) (MPa) (%) (MPa) Example 1 0.01 12.17 0.01 0.21 0.19 1.4 257 2.8 138 Example 2 0.01 12.36 0.21 0.20 0.19 0.9 283 3.3 147 Example 3 0.01 12.43 0.42 0.21 0.19 1.1 288 2.9 155 Example 4 0.01 12.50 0.62 0.21 0.19 1.2 295 2.3 176 Example 5 0.01 12.39 0.98 0.21 0.19 1.0 296 1.6 206 Example 6 0.00 12.46 0.22 0.15 0.40 0.8 Example 7 0.00 12.56 0.23 0.43 0.40 0.8 Example 8 0.00 12.56 0.21 0.45 0.40 1.1 Example 9 0.08 12.58 0.38 0.20 0.20 1.2 282 2.0 157 Comparative 0.01 12.59 0.00 0.65 0.00 2.8 Example 1 Comparative 2.18 10.81 0.24 0.65 0.03 26.0 354 3.4 184 Example 2 Comparative 0.04 0.56 3.49 0.47 0.02 1.1 272 18.1 142 Example 3 Comparative 0.00 8.65 0.58 0.46 0.00 2.2 Example 4 Comparative 0.00 6.11 0.45 0.46 0.00 2.5 Example 5 Comparative 0.05 6.09 0.46 0.45 0.00 2.2 Example 6 Comparative 0.10 6.00 0.45 0.45 0.00 3.0 Example 7 Comparative 0.30 6.05 0.45 0.45 0.00 9.4 Fxample 8 Comparative 0.50 6.00 0.45 0.44 0.00 14.1 Example 9

Table 2 shows the elemental compositions, liquidus temperatures, and flow lengths of aluminum alloys, which are the objects of the present invention, in Examples 10 to 14 and Comparative Examples 10 and 11.

TABLE 2 Liquidus Elemental composition temper- Flow (wt %) ature length Cu Si Mg Fe Cr (° C.) (mm) Notes Example 10 0.00 12.27 0.00 0.20 0.19 581 492 Approximate to Example 1 Example 11 0.00 12.38 0.19 0.21 0.20 582 494 Approximate to Example 2 Example 12 0.00 12.40 0.39 0.21 0.20 582 483 Approximate to Example 3 Example 13 0.00 12.54 0.59 0.21 0.21 584 482 Approximate to Example 4 Example 14 0.00 12.38 0.95 0.22 0.20 585 445 Approximate to Example 5 Comparative 1.90 10.76 0.20 0.84 0.08 571 330 Corresponding to Example 10 ADC12 Comparative 0.02 0.54 3.55 0.50 0.03 635 333 Corresponding to Example 11 ADC6

With reference to Table 1, as a result of the salt spray test, reduction in weight due to corrosion is not more than 1.4 mg/dm²/day in Examples 1 to 9 in which the content ratio of Cr with respect to the whole weight of the aluminum alloy is within a range of 0.10 to 0.50 wt %, whereas reduction in weight due to corrosion significantly exceeds 2.0 mg/dm²/day in Comparative Examples 1, 4 and 5 in which the content ratio of Cu is close to that in Examples 1 to 8 but Cr is not contained at all. This result indicates that the corrosion resistance is improved by containing Cr within the predetermined range described above.

When Examples 1 to 9 are compared with Comparative Example 2 corresponding to ADC12, it is found that the aluminum alloys of Examples 1 to 9 have corrosion resistances significantly higher than corrosion resistance of Comparative Example 2, and have mechanical properties approximately equal to mechanical properties of Comparative Example 2.

Further, with reference to Table 2, liquidus temperatures of Examples 10 to 14 (approximate to Examples 1 to 5) are significantly lower than liquidus temperature of Comparative Example 11 corresponding to ADC6, and are approximately equal to liquidus temperature of Comparative Example 10 corresponding to ADC12. In contrast, flow lengths of Examples 10 to 14 are significantly longer than those of Comparative Examples 10 and 11. That is, the aluminum alloys of the Examples 10 to 14 are superior in castability during die casting to the aluminum alloys of Comparative Examples 10 to 11. 

1. An aluminum alloy for die casting comprising: Cu by not more than 0.10 wt %; Si by 12.0 to 15.0 wt %; Mg by not more than 1.00 wt %; Fe by 0.05 to 1.00 wt %; Cr by 0.10 to 0.50 wt %; and a remaining portion thereof being Al and unavoidable impurities.
 2. The aluminum alloy for die casting according to claim 1, wherein at least one selected from Na, Sr, and Ca is added by 30 to 200 ppm.
 3. The aluminum alloy for die casting according to claim 1, wherein Sb is added by 0.05 to 0.20 wt %.
 4. The aluminum alloy for die casting according to claim 1, wherein Ti is added by 0.05 to 0.30 wt %.
 5. The aluminum alloy for die casting according to claim 1, wherein B is added by 1 to 50 ppm.
 6. An aluminum alloy die cast obtained through die-casting the aluminum alloy for die casting according to claim
 1. 